Self-healing, recyclable, and removable UV-curable coatings derived from tung oil and malic acid

Abstract

This study reports the development of super “green” smart coatings by integrating renewable resources, microwave-assisted synthesis, and dynamic covalent chemistry into UV-curable coatings. First, a novel UV-curable oligomer (TMG) was synthesized from renewable tung oil (TO) via microwave technology, and a biobased reactive diluent (MM) was derived from malic acid under ambient conditions. Afterward, a set of UV-curable coatings containing plentiful hydroxyl and ester groups were prepared by photo-polymerizing the TMG oligomer with the MM diluent. The resulting coatings demonstrated a high biobased content (49.2%–58.1%), good mechanical and thermal properties (e.g. T_g of 70.6–78.6 °C), and excellent coating adhesion and flexibility. Furthermore, by activating dynamic transesterification reactions at elevated temperatures with a zinc catalyst, the resulting UV-curable materials exhibited excellent repairability, removability, recyclability, malleability, and shape memory properties. For instance, the TMG material containing 10% of MM demonstrated a crack repair efficiency of 92.5%, a welding efficiency of tensile strength up to 171.8%, a recycling efficiency of tensile strength up to 404.3%, and a shape fixity ratio of 98.2%.